Ligament-tensioning device

ABSTRACT

Ligament-tensioning device for activation of the ligament and/or capsule system in the implantation of a joint implant, having a distal bearing plate for bearing against a distal skeletal part and having first and second proximal bearing plates, each of which partially overlaps the distal bearing plate in a first in-use position, for bearing against a proximal skeletal part, and having means for relative displacement of the proximal bearing plates to increase their spacing from the distal bearing plate. The displacement means have a scissor-type guide means that supports the respective proximal bearing plate in the ventral-dorsal as well as the medial-lateral parallel position with respect to the distal bearing plate.

The invention relates to a ligament-tensioning device for use in theimplantation of joint or skeletal implants in accordance with thepreamble of claim 1.

Ligament-tensioning devices having such a function are known. Forexample, WO 00/78225 A1 discloses a ligament-tensioning device which, inaddition to having a prismatic, cylindrical or plate-shaped base body,which has a bearing surface for bearing against a first bone adjoining anon-spherical joint, has right and left tensioning levers having secondbearing surfaces which are to be applied to the joint-side surface of asecond bone adjoining the joint, the operation of associated handgripsand operating levers being co-ordinated. The opposing portions (bearingsurfaces) are supported with respect to one another by four-bar levermechanisms.

DE 103 48 585 A1 discloses a further ligament-tensioning device whichcomprises a first, distal bearing plate for bearing against a firstskeletal part and a second, proximal bearing plate for bearing against asecond skeletal part, the two bearing plates being displaceable relativeto one another by a hydraulic drive means and, especially, beingtiltable relative to one another by means of a central axis. Inaddition, they are joined to one another by means of a base body, thedistal bearing plate in particular being joined rigidly thereto.

WO 2004/078047 A1 discloses a further ligament-tensioning device inaccordance with the preamble, which comprises a distal bearing plate andtwo proximal bearing plates independently guided and displaceablerelative thereto. Guidance is effected therein in each case by means ofa double hinge connection and the drive is preferably likewise effectedhydraulically.

According to current experiences, the known ligament-tensioning devicesstill have certain disadvantages in use. Those disadvantages relateespecially to the desired exact alignment between the opposing bearingplates and to the expense associated with a hydraulic drive device. Inaddition, when the known ligament-tensioning devices are used, the jointin question has to be kept open, because substantial parts of the deviceprotrude.

The invention is therefore based on the problem of providing an improvedligament-tensioning device having a wide variety of possibleapplications that is economical and reliably satisfies the requirementsof practice.

That problem is solved by a ligament-tensioning device having thefeatures of claim 1. The dependent claims relate to advantageousdevelopments of the inventive concept.

The invention includes the basic concept of providing aligament-tensioning device that is fully insertable into the joint inquestion, thus making it possible to close the joint capsule again afterinsertion. For that purpose, in particular the bearing plates are to bedimensioned to match the joint in question—for example a knee joint—andprojecting parts (such as, for example, handgrips/levers or hydrauliclines which project in the prior art) are to the greatest possibleextent to be avoided. In that respect the invention includes the conceptof providing a purely internal drive means or internal displacementmeans for the relative displacement of the opposing bearing plates.

In a preferred configuration, the invention includes the concept ofproviding parallel guidance between the distal bearing plate and theproximal bearing plates that is precise in both the ventral-dorsal andthe medial-lateral directions. The current view is that this can berealised especially advantageously by a suitable guide means inaccordance with the scissors principle. Other two-plane parallel guidemeans also come into consideration, however, for example the use of twohinge joints that are not axially parallel to one another (especiallyenclosing an angle of 90° with respect to one another).

In a relatively independent characterisation, the invention alsoincludes the concept of providing, as drive means for pushing the distalbearing plate and the proximal bearing plates apart from one another, aseparate drive element in each case, that drive element being, moreover,a drive element that functions without auxiliary energy. In thatcharacterisation, the invention includes finally the concept ofassigning to each proximal bearing plate a spring element which, in astarting state in which the proximal bearing plate is spaced a minimumdistance apart from the distal bearing plate, stores the drive energyand releases it for the purpose of increasing the spacing when theligament-tensioner is brought into operation. Finally, in a preferredconfiguration, the invention also includes the concept of assigning tothat spring element or to the opposing bearing plates a locking meansfor releasable fixing in the starting position.

In principle, however, a drive means having auxiliary energy, forexample an electromotive, electromagnetic, hydraulic or pneumatic drivemeans, also comes into consideration. Such a drive means can drive bothproximal bearing plates jointly, it being possible for the bearingplates to take up different end positions in force equilibrium with thesurrounding capsule/ligament structure. The said drive means can,however, also be provided separately for each proximal bearing plate.

It should be pointed out here that in the present description and theattached claims the terms “distal bearing plate” and “proximal bearingplate” are used with reference to preferred in-use positions of theligament-tensioner, for example when used in the knee. For thatapplication, it is also possible to speak synonymously of a tibiabearing plate and a femur bearing plate, respectively; the invention isalso to be understood, however, as expressly including transpositions ofthe bearing plates in respect of their position further from or closerto the centre of the body (distal or proximal, respectively).

In a configuration that is preferred from the current standpoint, thespring element has a compression spring element which is arranged in aregion of overlap between the proximal and distal bearing plates and issupported against both, the spring element having, especially, a steelor titanium helical spring having a suitable spring characteristic. Itis distinguished by a spring constant matched to a predeterminedtensioning force in order to provide, especially, a tensioning forcethat is substantially constant over its travel in the range between 50and 90 N, especially 70 N.

In view of the special requirements of realising a relatively high andconstant tensioning force and realising as small as possible an initialheight of the spring element in the tensioned state, it is preferable touse special forms of the compression springs that are tailored thereto.A preferred form from the current standpoint is distinguished by thefact that the steel or titanium helical spring for increasing the travelis of conical or double-cone form and, especially, has a pitchindirectly proportional to the local winding diameter. The conical shapeof the spring element is so chosen that the overall height in thetensioned state is substantially less than that of a comparable helicalspring having a cylindrical basic shape.

In an alternative configuration, the spring element has a flexuralspring element, more specifically, for example, a steel spiral or leafspring.

The scissor-type guide means preferred as the parallel guide meanspreferably has two scissor joints arranged close to opposite ends of theproximal bearing plate, that is to say spaced as far apart from oneanother as possible. In various configurations of the invention it ispossible for those scissor joints to be arranged in the ventral-dorsaldirection (one behind the other) or in the medial-lateral direction (onenext to the other). In an advantageous configuration of the scissor-typeguide means, the ends of the scissor joints are inserted in grooves inthe distal and proximal bearing plates and a limb or an end of each ofthe two limbs is rotatably fixed therein by means of bearing pinsextending perpendicular to the run of the groove.

Additionally improved guidance and fixing to one another of the opposingbearing plates is obtained by providing at each end of the free limb orat the free end of each of the two limbs a slide peg for guiding therespective limb or end in a groove formed to match the slide peg. Toincrease the rigidity and to provide even better guidance, the scissorjoints are preferably also joined to one another by means of at leastone connecting rod mounted at the end of a limb of each scissor joint.

For adaptation to the specific anatomical conditions of differentpatients, the first and second proximal bearing plates each comprise anupper and a lower part, the lower part being provided with means formounting the spring element and the scissor-type guide means and theupper part being fixed releasably on the lower part to increase thethickness of the bearing plate in question. The ligament-tensioningdevice can be used with a set of upper parts of different thicknesses toprovide an especially precise solution to the mentioned adaptationproblem.

The above-mentioned locking is advantageously released by the provisionon the distal bearing plate or the first and second proximal bearingplates of releasable locking means for independent locking of the firstand second proximal bearing plates to the distal bearing plate at aminimum spacing and with a maximum spring tension with respect thereto.

A preferred construction is obtained when the locking means each have ahook pivotally mounted on the respective bearing plate and engaging inthe opposing bearing plate, on which hook there is provided a firsttool-engagement portion for actuation. In view of the armoury of toolsavailable in the field of application of the proposed ligamenttensioner, the tool-engagement portion is preferably configured forengagement of a hex key tool, for example a 3.5 mm hex key.

In a first configuration of the locking means having a pivotable hook,an engagement portion for that hook is formed in the material of thefirst and second proximal bearing plates in spatial association with thehook articulated on the distal bearing plate.

In a second configuration, a first bearing peg of a scissor joint of thefirst and second proximal bearing plates projects beyond the outer edgethereof and is so arranged relative to the hook pivotally mounted on thedistal bearing plate that it forms a counter-bearing of the lockingmeans. In that configuration—or alternatively independently thereof—in apractical structural solution a second bearing peg of a scissor joint ofthe first and second proximal bearing plates projects beyond the outeredge thereof and is so arranged relative to the hook pivotally mountedon the distal bearing plate that it forms the hinge pin thereof

Since, on account of the high forces necessary, a tool is alsoadvantageously used for positioning the ligament tensioner at the siteof use, a second tool-engagement portion, especially a cylindricalrecess, is preferably provided on the side edges of the distal bearingplate and of the first and second proximal bearing plates for engagementof a positioning tool. The provision of a separate tool is especiallyadvantageous with a view to realising a ligament tensioner that can befully integrated into a joint.

A further advantageous configuration provides a construction for thereleasable coupling-on of a sizer, which couples the proximal and distalskeletal parts in flexion so that axis transmission from the oneskeletal part to the other, taking account of the ligament tension, ispossible. In principle, the coupling-on also covers simply being incontact with suitably prepared bearing surfaces, but it preferablyincludes connecting means for fixing the sizer on the distal bearingplate. In a configuration that is advantageous from the currentstandpoint, the connecting means comprise two clip-like extensions onthe distal bearing plate which, each engaging around a side edge of theproximal bearing plates, run to a base plate of the sizer.

Arrangements comprising the proposed ligament-tensioning device and amatching positioning tool and/or a sizer matched thereto are also to beregarded as being included in the scope of protection of the invention.

Advantages and functional features of the invention will otherwise befound in the dependent claims and in the following description ofpreferred exemplary embodiments with reference to the Figures:

FIG. 1 is a perspective view of a ligament-tensioning device accordingto the invention ventrally obliquely from above, partly as an explodedview, with an attached positioning tool,

FIG. 2 is a perspective view of the ligament-tensioning device accordingto FIG. 1 ventrally obliquely from above, with the second proximalbearing plate removed and the associated displacement means in the fullyextended state;

FIG. 3 is a perspective view of the ligament-tensioning device accordingto FIG. 1 and 2, with the second proximal bearing plate removed and thedisplacement means in an intermediate position, dorsally obliquely fromabove,

FIG. 4 is a perspective view of the ligament-tensioning device accordingto FIG. 1-3, with the second proximal bearing plate removed, ventrallyobliquely from below,

FIG. 5 is a perspective view of a helical spring suitable for use asspring element in the ligament-tensioning device according to FIG. 1-4,in a double-cone configuration,

FIG. 6A-6D show various views of the ligament-tensioning deviceaccording to FIG. 1 in its in-use state installed in a knee joint, and

FIG. 7A-7D show various views of the ligament-tensioning deviceaccording to FIG. 1 in its in-use state installed in a knee joint, witha coupled-on sizer.

FIG. 1-4 show various views of a ligament-tensioning device 1 in variousstates, with FIG. 1 showing the device co-operating with a positioningtool.

The ligament-tensioning device 1 comprises a distal bearing plate 5,which is approximately kidney-shaped in plan view, and, arranged inparallel therewith and opposite thereto, two proximal bearing plates 7and 9 each of which overlaps approximately half of the distal bearingplate, the proximal bearing plates each comprising a lower part 7 a, 9 aand an upper part 7 b, 9 b. For positioning the ligament-tensioningdevice 1 with the aid of the positioning tool 3 there are provided onthe front side edges of the distal and proximal bearing platesrespective cylindrical recesses 11 as engagement portions (FIG. 1 showsthe recesses in the proximal bearing plates, more specifically in theupper parts 7 b, 9 b thereof, while FIG. 2 shows the central recess 11in the distal bearing plate 5).

The proximal bearing plates 7 and 9 (or, more specifically, the lowerparts 7 a, 9 a thereof) are joined to one another by means of ascissor-type guide means 13 and are tensioned against one another by asteel compression spring 15 as spring element. As can be seen mostclearly in FIG. 2 and 3, the helical spring 15 is seated in a matchingcircular recess 17 on the upper side of the distal bearing plate 5; asimilar mounting (not shown) is provided on the underside of therespective associated proximal bearing plate.

The scissor-type guide means 13 comprises medial and lateral scissorjoints 19, 21 which each comprise two limbs 19 a, 19 b and 21 a, 21 bpivotally connected by means of a hinge pin 23, 25, respectively. Thelimbs 19 a, 21 a are joined to one another at one end by means of anintegrally formed bridge or connecting bar 27, while a slide peg or pin29 a, 31 a is inserted in their other end for connection to the lowerpart 9 a (omitted in FIG. 2 and 3) of the second bearing plate. In asimilar way, one end of each of the limbs 19 b, 21 b is joined by meansof a connecting rod 33 inserted perpendicular to the plane of extension,which rod projects beyond the medial or lateral outer side of therespective limb and forms further slide pegs (not shown separately)there.

The opposite ends of the limbs 19 b, 21 b are in turn each provided witha separate slide pin 29 b, 31 b, respectively. Those slide pegs 29 b, 31b engage (as can be seen most clearly in FIG. 3) in correspondinglydimensioned grooves 35, 37 in the distal bearing plate 5 which, in thein-use position of the ligament-tensioning device, rundorsally-ventrally and fix the scissor-type guide means so as to beslidable therewith in the distal bearing plate 5. (As can be seen tosome extent in the portion of FIG. 3 showing the lower part 7 a of thefirst proximal bearing plate 7—see detail “A”—a corresponding groovestructure, which does not have a separate reference numeral herein, isprovided in the proximal bearing plates.)

As can be seen most clearly in FIG. 2, on the ventral side edge (frontedge) of the distal bearing plate 5, on both sides of an extensioncontaining the cylindrical recess 11 there are mounted two pivotablehook elements 41, 43, each of which comprises a hex key engagementportion 41 a, 43 a and an integrally formed hook portion 41 b, 43 b,respectively. As can be seen in FIG. 2 in the region of the firstproximal bearing plate, the hook portions engage in a recess on theupper side of the respective bearing plate lower part, which recess isshaped to correspond to the shape of the hook, only the recess 45 in thelower part 7 a of the first proximal bearing plate being shown in FIG.2. By means of such engagement, the proximal bearing plates are held ata minimum distance from the distal bearing plate. By rotation of therespective hook element 41, 43 with a suitable tool, that locking isreleased and the proximal bearing plate in question can be moved awayfrom the distal bearing plate under the bias of the associatedcompression spring 15 until its movement comes to a standstill in forceequilibrium with the capsule/ligament tension acting at the site of use.

Whereas in FIGS. 1-4 a cylindrical helical spring 15 is shown as thespring element, FIG. 5 shows, as a modification, a double-cone helicalspring 15′ which, by virtue of its lesser overall height in thetensioned state, can be used preferably in the ligament-tensioningdevice 1 according to FIG. 1-4, it being possible (in a configurationnot shown) for the pitch of the winding in the lower and upper regionsof greater diameter to be smaller than in the central region, in orderthat a troublefree spring action is ensured over the entire travel.

The above-described ligament-tensioning device 1 is constructed for usein a knee joint and is shown in that in-use state in various views inFIG. 6A to 6D. The Figures clearly show the matching of the dimensions,especially the length/ width ratio, and the configuration of the twoproximal bearing plates 7, 9 to the anatomical conditions of the kneejoint and specifically the overall dimensions and relative sizes of thetibia T and the (resected) femur F.

FIG. 7A to 7D show a diagrammatic view, comparable to FIG. 6A-6D, of amodified configuration of a ligament-tensioning device 1′ with acoupled-on sizer 47. As is known, a sizer serves for the intra-operativecoupling of tibia and femur in flexion so that axis transmission of thetibial axis, taking account of the ligament tension, to the femur can beeffected. It is accordingly possible, in addition, to define the optimumsize and position of a knee implant in the ventral-dorsal direction andin rotation. The technical features of the sizer are not the subjectmatter of the present invention and are therefore not described herein.Attention should be drawn, however, to the provision of connecting meansbetween the ligament-tensioning device 1′ and the sizer 47, namely twoclip-like extensions or connecting bars 49 a, 49 b on the distal bearingplate 5, which engage over the proximal bearing plates (not shownherein) at one side edge thereof and make a connection to a base plate51 of the sizer 47.

The implementation of the invention is not confined to the exemplaryembodiment described herein and the last-mentioned modification of thespring element, but is also possible in a multiplicity of modificationswhich lie within the scope of technical action. For example, inparticular a configuration is possible having a scissor-type guide meanswhich is turned through 90° with respect to the embodiment shown and inwhich some of the slide pegs or pins can be constructed simultaneouslyas bearing pins for the fixed positioning of a limb end in theassociated bearing plate. In such a configuration it is also possiblefor such a bearing pin to be used simultaneously as hinge pin of thepivotable locking hooks. Furthermore, in the case of the proximalbearing plates it is also possible for the upper parts to be omitted,and numerous degrees of freedom exist in respect of the exact shape andrelative dimensions of the bearing plates.

List of Reference Numerals

-   1 ligament-tensioning device-   2 positioning tool-   5 distal bearing plate-   7, 9 proximal bearing plates-   7 a, 9 a lower parts of the proximal bearing plates-   7 b, 9 b upper parts of the proximal bearing plates-   11 cylindrical recess-   13 scissor-type guide means-   15 cylindrical helical spring-   15′ double-cone helical spring-   17 circular recess-   19 medial scissor joint-   19 a, 19 b limbs of the medial scissor joint-   21 lateral scissor joint-   21 a, 21 b limbs of the lateral scissor joint-   23 hinge pin of the medial scissor joint-   25 hinge pin of the lateral scissor joint-   27 connecting bar-   29 a, 29 b, 31 a, 31 b slide pegs-   35, 37 grooves-   41, 43 hook elements-   41 a, 43 a hex key engagement portions-   41 b, 43 b integral hook portions-   45 recess-   47 sizer-   49 a, 49 b extensions-   51 base plate

1-30. (canceled)
 31. A ligament-tensioning device for activation of theligament and/or capsule system in the implantation of a joint implant,said device comprising: a distal bearing plate adapted to bear against adistal skeletal part; first and second proximal bearing plates, each ofwhich at least partially overlaps said distal bearing plate when in afirst in-use position, and adapted to bear against a proximal skeletalpart; a displacer for relative displacement of said proximal bearingplates away from the distal bearing plate so as to increase theirspacing from the distal bearing plate; and wherein the components ofsaid ligament-tensioning device are dimensioned such that they can beaccommodated between portions of the distal and proximal skeletal partsadjacent to the joint such that a joint capsule can be closed againafter insertion of the ligament-tensioning device.
 32. The device ofclaim 31, wherein the distal skeletal part is a tibia and the proximalskeletal part is a femur.
 33. The device of claim 31, wherein thecomponents include the distal bearing plate and the first and secondproximal bearing plates.
 34. The device of claim 31, wherein thedisplacer is an internal displacer.
 35. The device of claim 31, whereinthe displacer further comprises scissor-type guides that support therespective proximal bearing plates in a parallel position with respectto the distal bearing plate.
 36. The device of claim 35, wherein thescissor-type guides are of torsionally stiff construction between thedistal bearing plate and the respective proximal bearing plates toprovide parallel guidance between the distal bearing plate and theproximal bearing plates that is precise in both the ventral-dorsal andthe medial-lateral directions.
 37. The device of claim .31, wherein saiddisplacer comprises at least one spring element adapted to drive saidproximal bearing plates, the spring element configured to store a driveenergy while in a starting state in which said proximal bearing platesare spaced a minimum distance apart from said distal bearing plate, andto release said energy to increase the spacing when the device isactuated.
 38. The device of claim 37, wherein said displacer has,assigned to each of said first and second bearing plates, a springelement for driving each of said proximal bearing plates.
 39. The deviceof claim 37, wherein the at least one spring element is lockable. 40.The device of claim 37, wherein the at least one spring elementcomprises a compression spring element arranged in a region of overlapbetween said proximal and distal bearing plates.
 41. The device of claim40, wherein said at least one spring element comprises a spring selectedfrom the group consisting of a steel helical spring and a titaniumhelical spring which has a form selected from the group consisting of aconical form and a double-cone form.
 42. The device of claim 41, whereinsaid spring comprises a pitch indirectly proportional to a local windingdiameter.
 43. The device of claim 37, wherein said spring elementcomprises a flexural spring element.
 44. The device of claim 43, whereinsaid spring element comprises a metal spring selected from the groupconsisting of a spiral spring and a leaf spring.
 45. The device of claim35, wherein said scissor-type guide comprises two scissor jointsarranged close to opposite ends of said proximal bearing plate.
 46. Thedevice of claim 45, wherein the ends of the scissor joints are insertedin grooves in said distal and proximal bearing plates and one limb ofeach scissor joint or an end of one limb of each scissor joint isrotatably fixed within the plates by bearing pins or slide pegsextending perpendicular to a run of said groove.
 47. The device of claim46, wherein on another end of the limb or at a free end of another limbthere is provided a slide peg for guiding the respective limb or end ina groove in said distal or proximal bearing plate, which groove isformed to match the slide peg.
 48. The device of claim 45, wherein saidscissor joints are joined to one another at least by a connecting rodmounted at the end of a limb of each scissor joint.
 49. The device ofclaim 31, wherein said first and second proximal bearing plates eachcomprise an upper and a lower part, the lower part comprising a mountingadapted to mount at least one of said scissor-type guide and said springelement, the upper part being fixed releasably on the lower part toincrease, as desired, the thickness of the bearing plate in question.50. The device of claim 31, wherein the distal bearing plate or thefirst and second proximal bearing plates comprise releasable lockingdevices for independent locking of said first and second proximalbearing plates to said distal bearing plate at a minimum spacing andwith respect thereto.
 51. The device of claim 50, wherein said lockingdevice has a hook pivotally mounted on the respective bearing plate andengaging in an opposing bearing plate, on which hook there is provided afirst tool-engagement portion for actuation.
 52. The device of claim 51,wherein the first tool-engagement portion is formed for engagement of ahex key.
 53. The device of claim 51, wherein in the material of saidfirst and second proximal bearing plates, in spatial association withthe hook articulated on said distal bearing plate, there is formed anengagement portion for the hook.
 54. The device of claim 51, wherein afirst bearing peg of a scissor joint of the first or second proximalbearing plate projects beyond an outer edge thereof and is so arrangedrelative to the hook pivotally mounted on said distal bearing plate thatit forms a counter-bearing of the locking device.
 55. The device ofclaim 51, wherein a second bearing peg of a scissor joint of said firstor second proximal bearing plates projects beyond the outer edge thereofand is so arranged relative to the hook pivotally mounted on said distalbearing plate that it forms a hinge pin thereof.
 56. The device of claim31, further comprising a cylindrical recess or other secondtool-engagement portion, provided on the side edges of the distalbearing plate or of the first and second proximal bearing plates forengagement of a positioning tool.
 57. The device of claim 37, having aspring element matched in spring constant to a predetermined tensioningforce.
 58. The device of claim 57, wherein the spring element provides atensioning force that is substantially constant over its travel.
 59. Thedevice of claim 58, wherein the tensioning force is in the range ofbetween 50 and 90 N.
 60. The device of claim 58, wherein the tensioningforce is approximately 70 N.
 61. The device of claim 31, wherein thelength/width ratio of the device generally matches the proportions of aresected portion of the adjacent skeletal part close to the joint. 62.The device of claim 31, comprising a configuration generally matched toa knee joint, the adjacent skeletal parts being a femur and a tibia. 63.The device of claim 61, wherein the length/width ratio is approximately3/2 in accordance with that of a proximal resected tibia.
 64. The deviceof claim 31, wherein at least one of the bearing plates is releasablycoupleable to a sizer, which couples the proximal and distal skeletalparts in flexion to allow axial transmission from the one skeletal partto the other, taking account of the ligament tension.
 65. The device ofclaim 64, having a connecting device for attaching the sizer on thedistal bearing plate.
 66. The device of claim 65, wherein the connectingdevice comprises two clip-like extensions on the distal bearing platewhich, each engaging around a side edge of the proximal bearing plates,run to a base plate of the sizer.
 67. A ligament-tensioning systemcomprising a ligament-tensioning device for activation of the ligamentand/or capsule system in the implantation of a joint implant and a sizerto be attached to said device, said device comprising: a distal bearingplate adapted to bear against a distal skeletal part; at least oneproximal bearing plate, which at least partially overlaps said distalbearing plate in a first in-use position, and is adapted to bear againsta proximal skeletal part; and a displacer for relative displacement ofsaid proximal bearing plate relative to the distal bearing plate toincrease their spacing from the distal bearing plate; wherein componentsof said ligament-tensioning device, including the distal bearing plateand proximal bearing plate, are dimensioned so as to be entirelyaccommodated between portions of the distal and proximal skeletal partsadjacent to the joint in such a way that a joint capsule can be closedagain after insertion of the ligament-tensioning device and a sizer. 68.The system of claim 67, wherein said ligament-tensioning device and saidsizer are releasably coupled together and generally sized to match aknee joint implant.
 69. The system of claim 67, wherein saidligament-tensioning device comprises two proximal bearing plates, eachindependently displaceable relative to the distal bearing plate.
 70. Thesystem of claim 67, wherein the proximal skeletal part is a femur andthe distal skeletal part is a tibia.
 71. A method of putting a ligamentin tension comprising: resecting a joint surface of at least one of atibia and a femur; inserting a ligament-tensioning device having atleast one distal bearing plate and at least one proximal bearing plateinto a space between the tibia and femur, the device inserted in a firstcompact configuration, at least one of said plates disposed adjacent tothe resected joint surface; displacing the at least one proximal bearingplate away from the at least one distal bearing plate so as to move thedevice into a second expanded configuration to increase a space betweenthe tibia and the femur; and closing a joint capsule connecting thetibia and femur to enclose the bearing plates.
 72. The method of claim71, wherein the joint capsule is closed prior to displacing the at leastone proximal bearing plate away from the at least one distal bearingplate.
 73. The method of claim 71, wherein the ligament-tensioningdevice fuirther comprises at least one displacer between the proximaland distal bearing plates, for displacing said proximal and distalbearing plates away from each other.
 74. The method of claim 73, whereinthe at least one displacer comprises a spring element.
 75. The method ofclaim 73, further comprising the step of actuating the at least onedisplacer.
 76. The method of claim 71, wherein the step of displacingcomprises mechanically displacing.
 77. The method of claim 73, whereinthe at least one displacer comprises a plurality of displacers that canbe activated independently.
 78. The method of claim 71, whereinresecting comprises resecting both the femur and tibia.
 79. The methodof claim 73, wherein the at least one displacer is activated by theinteraction of a hex key and an engagement portion of at least onebearing plate.
 80. The method of claim 71, wherein the plates arepositioned by a positioning tool that engages a cylindrical recess on atleast one of the side edges of the at least one distal bearing plate andthe at least one proximal bearing plate.
 81. The method of claim 72,wherein prior to the closing step a sizer is releasably attached to adistal bearing plate after being inserted between the femur and tibiaand configured to define a preferable size for the at least one proximalbearing plate.